The present invention relates to a method for the control of the opacity of the exhaust of the combustion of solid fuel and air in a furnace, and more particularly, to a method of reducing the opacity of the exhaust of said combustion.
As environmental concerns have increased with regard to the discharge of waste products of combustion from a furnace, increasing attention has been focused on the level of opacity of the exhaust produced by these furnaces. At the same time, however, the recent price increases initiated by the Oil Producing Exporting Countries (OPEC) has led to an increasing awareness of the diminishing world supply of liquid fossil fuels. On the other hand, the world reserve of solid fuel, such as coal, bark, etc., is at present estimated to be much larger than the world reserve of liquid fossil fuel. The use of these solid fuels, in light of the environmental restraints, impose certain conditions in the control of the opacity of the exhaust of the combustion of the solid fuel and the air in the furnace.
Heretofore, the control of the opacity of the exhaust of combustion of solid fuel and air in a furnace has been simple and straightforward, based upon intuition. The control strategy is simply to increase the air, in the event the measured opacity level is greater than that desired and conversely to decrease the amount of air in the event the measured level of opacity is lower than that desired. It has been found, however, that while this simple and intuition-based method works well for the combustion of liquid or gaseous fossil fuel and air in a furnace, the control of the opacity of the exhaust of the combustion of solid fuel and air in a furnace necessitates a different method.